Process of forming mosaic phosphor screen of color picture tube

ABSTRACT

A flat electric winding is disposed slightly above the face plate of shadow mask color picture tubes. The face plate is positioned on a known apparatus including a correction lens to print a mosaic of color phosphor dots on the internal surface of the face plate. A high frequency current flows through the winding to heat the associated shadow mask to somewhat thermally deform it. A beam of ultraviolet radiation from a point source of radiation irradiates the internal surface of the face plate through the lens and deformed shadow mask to print a mosaic of color phosphor dots for each primary color on the surface.

United States Patent 1 [451 Nov. 26, 1974 Fujimura et a1.

[73] Assignee: Mitsubishi Denki Kabushiki Kaisha,

Tokyo, Japan [22] Filed: July 20, 1972 [21] Appl. No.: 273,459

[30] Foreign Application Priority Data July 27, 1971 Japan 46-56288 [52] US. Cl. 117/335 CM, 96/36.1, 313/92, 313/109 [51] Int. Cl C036 3/28, C03c 17/00, HOlj 1/54 [58] Field of Search 117/335 CM, 101; 313/92, 313/109;96/96.1

[56] References Cited UNITED STATES PATENTS 3,615,462 10/1971 Szegho et a1 96/36.1

3,653,939 4/1972 Prazak 117/335 CM Primary Examine/-Wi1liam D. Martin zlssistant Examiner-William R. Trenor Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [5 7 ABSTRACT A flat electric winding is disposed slightly above the face plate of shadow mask color picture tubes. The face plate is positioned on a'known apparatus including a correction lens to print a mosaic of color phosphor dots on the internal surface of the face plate. A

' high frequency current flows through the winding to heat the associated shadow mask to somewhat thermally deform it. A beam of ultraviolet radiation from a point source of radiation irradiates the internal surface of the face plate through the lens and deformed shadow mask to print a mosaic of color phosphor dots for each primary color on the surface.

3 Claims, 14 Drawing Figures PATENTEL 40V 2 6 I974 SHEET 10F 2 FIG. 3

4 22 20 46 Hl-FREQ u. oscu: 0/ 40 LATOR g:&e\

' 14 LAMP 1 HOUSE FIG. 40 4 L FIG. 4b

v PROCESS OF FORMING MOSAIC PHOSPHOR SCREEN OF COLOR PICTURE TUBE BACKGROUND OF THE INVENTION rection lens for each of the three primary colors dis-' posed transversely to an optical path along which a beam of light emanating from a point source of light travels through the shadow mask toward the face plate. The correction lenses have complicated configurations so that the designand production thereof time consuming and requires a great amount of labor. Also as color picture tubes as a whole are constantly being improved, it has been necessary for the correction lens to be correspondingly modified in structure. This is time consuming and very expensive because the correction lens is first modified in design, then constructed for trial and the test lens thus constructed is used to produce test color picture-tubes which requires testing of the tubes. The process as above described is repeated by trial and error until a collection lens having satisfactory properties constructed for mass production. Therefore it is highly desirable to form each element of mosaic phos- BRIEF DESCRIPTION OF THE DRAWINGS The invention will become readily apparent from the following detailed, description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a schematic elevational view, partly in vertical section of an apparatus for printing a mosaic of phor screen in a predetermined position on the face plate of color picture tubes without the necessity of changing the design of the correction lenses.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide a new and improved process of forming the mosaic phosphor screen of shadow mask color picture tubes which minimizes the mislanding of electrons on the screen throughout the entire area.

It is a special object of the invention to provide a new and improved process of forming the mosaic phosphor screen in a predetermined pattern on the face plate of color picture tubes without the necessity of modifying the design of the correction lenses involved.

The invention accomplishes these object by the provision of a process of forming mosaic phosphor screen of a shadow mask color picture tube, comprising the steps of positioning a shadow mask inside a face plate having an internal surface coated with a layer of phosphor material, irradiating the layer of color phosphor material with the beam of radiation through holes on the shadow mask to print color phosphor dots in a predetermined pattern on the internal surface of the face plate. characterized in that heating means is disposed on the outside of the face plate to heat the shadow mask to cause a predetermined thermal deformation of the latter while the beam of radiation irradiates the internal surface of the face plate.

Preferably the heating means may be a flat electric winding through which a high frequency current flows to heat the shadow mask.

Advantageously the high frequency current may vary in waveform or amplitude to adjust a temperature to which the shadow mask is heated.

phosphor dots on the face plate of shadow mask color picture tubes in accordance with the principles of the prior art with the face plate partly broken away;

FIG. 2 is a longitudinal sectional view of a shadow mask color picture tube useful in explaining the man- 'ner in which a beam of electrons impinges upon the proper screen area;

FIG. 3 is a schematic elevational view, partly in vertical section of an apparatus for printing mosaic of phosphor dots on the face plate of shadow mask color picture tubes in accordance with the principles of the invention with the face plate partly broken away.

FIG. 4a is a schematic plan view of the face plate as shown in FIG. 3 illustrating the positional relationship between the face plate and the heating winding shown in FIG. 3;

FIG. 4b is a view similar to FIG. 4a but illustrating a modification of the heating winding;

FIG. 5 is a fragmental sectional view of one portion of the color picture tube shown in FIG. 3 and illustrating a change in a position on the screen where a particular screen mosaic is to be printed, caused from the invention;

FIGS. 6a is a diagrammatic view illustrating directions in which positions for phosphor dots are displaced with the arrangement shown in FIG. 4a;

FIG. 6b is a view similar to FIG. 60 but corresponding to the arrangement shown in FIG. 4b;

FIG. 7a is a fragmental plan view of mosaic screen having disposed thereon a layer of non-luminescent material including a multiplicity of blank areas in a predetermined pattern which area are subsequently filled with phosphor dots in accordance with the method of the invention; I

FIG. 7b is a fragmental sectional view of a mosaic phosphor screen including phosphor dots filling the blank areas shown in FIG. 7a;and

. FIGS. 8a and d are sectional views illustrating steps of forming the mosaic screen shown in FIG. 7a.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and FIG. I in particular, there is illustrated an apparatus for printing a mosaic of color phosphor dots in a predetermined pattern on the face plate of shadow mask color picture tubes. The arrangement illustrated comprises a framework 10, and a lamp house 12 disposed on the lower portion of the framework 10. The reference numeral 14 designates a point source of radiation disposed above the lamp house 12. The point source 14 actually acts as a divergent point for radiation through which a radiation, in this case, ultraviolet radiation produced in the lamp house 12 is divergently emitted in the upward direction as viewed in FIG. I toward a correction lens 16 disposed on the upper portion of the framework 10.

The frontportion of a shadow mask color picture tube is shown in FIG. I as including a front face 18 disposed on the upper surface of the framework 10, a layer of phosphor slurry 20 for the particular color applied to the internal surface of the front plate 18 and a shadow mask 22 fixedly secured to the internal surface of the front plate 18 through a holding mechanism 24 including a frame 26. As is well known, the phosphor slurry forming the layer 20 has a suitable photo sensitive material intimately mixed therewith and the shadow mask 22 is formed of a metallic sheet having a configuration complementary to the internal surface of the front plate 18 and provided with a multiplicity of minute holes in a predetermined pattern. The holes are very exaggeratedly shown for purposes of illustration. Positioning claws 28 (only one of which is illustrated) are used to fasten the front plate 18 on the upper surface of the framework in its predetermined position with respect to the point source 14 with that portion of the upper framework surface facing the internal surface of the front plate 18 being removed to form an opening (not shown).

The divergent beam of ultraviolet radiation from the source 14 leaving the correction lens 16 passes through the multiplicity of minute holes on the shadow mask 22 and reaches those areas of the layer of phosphor slurry operatively associated with the respective holes on the shadow mask 22. Those areas ofthe layer 20 irradiated with the ultraviolet radiation cause a photochemical action to form a latent image for a mosaic of the particular color phosphor dots for the particular color. By suitably processing the layer 20 thus irradiated, the mosaic of phosphor dots is formed on the internal surface of the front plate 18.

The front plate 18 has generally a triad of phosphor mosaics disposed in predetermined patterns on the internal surface thereof and adapted to emit light in assigned ones of three primary colors in response to the impingement of electrons thereon. To this end, it has been commonly practiced to go through the step of forming the phosphor mosaic as above described three successive times, once for each of three different-color phosphor slurrys, by using three separate printing apparatus as above described which have slightly different parameters from one another. The face plate I8 having a triad of color phosphor mosaics thus formed thereon is assembled in one color picture tube along with the shadow mask 22, the holding mechanism 24 with the frame 26 operatively associated with that .face plate during the formation of the mosaic.

FIG. 2, wherein like reference numerals designate the components identical to those shown in FIG. 1, illustrates a shadow mask color picture tube assembled as above described. While the color picture tube actually has a triad of color phosphor mosaics disposed on the internal surface of the front plate thereof, FIG. 2 illustrates merely one of the mosaics in exaggerated fashion for purposes of illustration. As shown in FIG. 2, the face plate 18 has, disposed on the internal surface, a phosphor mosaic 200 corresponding to one of the three primary colors or red, green or blue and is physically connected to a so-called funnel portion 30 to form an evacuated envelope for the color picture tube. The funnel portion 30 is connected at the smaller diameter end to a hollow cylindrical portion or a neck portion in which three electron guns are disposed one for each of red, green and blue colors. However, FIG. 2 shows in block only one of the three electron guns 32A corresponding to the phosphor mosaic 20a for one of the three primary color.

In operation, a electron beam is emitted from the electron gun 32a and is deflected by a deflecting yoke 34 disposed around the transition region of the envelope from the cylindrical to the flared portion. More specifically, the deflecting yoke 34 establishes a pair of horizontal and vertical magnetic fields consistently varied in field strength with time so that the electronbeam designated by the reference numeral 36 is caused to substantially uniformly scan the entire surface of the shadow mask 22 facing the electron gun 32a. Under these circumstances, the greater portion of the electrons in the electron beam from the electron gun 32a impinge on the solid portion of the shadow mask 22 and only a small portion thereof pass through the holes in the shadow mask 22 and impinge upon the associated phosphor dots of the mosaic 20a whereupon those dots emit light in the assigned color.

In order to satisfactorily operate the shadow mask color picture tube as shown in FIG. 2, it is required to cause those electrons passing through each hole on the shadow mask 22 to precisely land on the proper phosphor dot. Thus one should preliminarily determine whether the electrons in the electron beam passing through the associated holes on the shadow mask will impinge precisely upon the regions where corresponding color phosphor dots are printed to form one of the phosphor mosaics.

For this purpose, the correction lens 16 has been disposed below in the shadow mask as shown in FIG. I. With point source l4 stationary to directly irradiate the shadow mask 22, it is impossible to form each of color phosphor mosaics having color phosphor dots printed at their positions on which the electrons in the associated beam are to impinge after having passed through the holes on the shadow mask. To avoid this serious objection, the correction lens 16 has been utilized to direct the beam of ultraviolet radiation from the point source 14 through each hole on'the shadow mask 22 to the desired position associated with each hole on the internal face surface throughout the entire area whereby the particular color phosphor dots can be printed at the positions thus obtained. If the resulting phosphor mosaic includes some of its phosphor dots at positions even slightly shifted from the desired positions on which the associated beam of electrons is to impinge, the mosaic is deemed misregistered. The purpose of the correction lens 16 is to substantially eliminate or minimize this misregistration of the phosphor mosaic relative to the electron target positions.

Conventional processes and apparatus previously employed to print phosphor mosaics as above described have included the correction lens. The design and manufacture thereof has consumed a great deal of time and required a great amount of labor which has been one of the disadvantages.

Therefore once a correction lens has been designed and produced to be as small in misregistration as possible for a given type ofshadow mask color picture tubes, it is desirable to ensure that there is no need for modification of the correction lens. However, the fact is, that the correction lens is continuously required to be modified because color picture tubes are being increasingly improved.

As an example, a change in design of the deflecting yoke leads to the necessity of varying the design of the correction lens involved. As seen in FIG. 2, the deflecting yoke 34 is what most affects the orbit of-the electron beam formed in picture tubes in operation. And the deflecting yoke per se has many problems in conjunction with television re'ceivers. This may occasionally lead to an inevitable change in design of the yoke and therefore of the correction lens. I

As another example, the correction lens may be required to change in design in accordance with a variation in design of the shadow mask and its holding mechanism including the frame. The shadow mask and those associated components may be simply called the shadow mask hereinafter. As above described, most electrons in an electron beam from an electron gun impinge upon the shadow mask and only some pass through the holes thereon to impinge upon the associated areas of phosphor mosaic on the face plate. As a result, the shadow mask disposed in picture tubes increases in temperature during the operation thereof and becomes slightly deformed. This results in a change in misregistration characteristic. The correction lens is generally designed and constructed in conjunction with a particular shadow mask after having been deformed due to the operation of the associated color picture tube. This measure will results in an undesirable temporary misregistration occurring during the initial operation of the tube which continues until it is stable in operation.

In order to eliminate that temporary misregistration, the shadow mask along with its materials may sometime change in design. Therefore one must modify the particular correction lens designed and constructed for a given thermal deformation of the shadow mask involved.

Further, it may be required to manufacture new color picture tubes somewhat different in size from the existing color picture tubes. For example, while 20 inch color picture tubes have been manufactured it may be necessary to produce 22 inch tubes identical in deflection angle to the 20 inch tubes. In that event it has been the common practice to design and construct a new correction lens for each of the primary colors because evacuated envelopes (which include the face plate and funnel 18 and 30 respectively) change in deformation from the previous ones due to the presence of a vacuum in the envelope. I Y I However the design of the correction lens is very troublesome. In addition, the lens must be constructed by trial and error in accordance with its design which are used to produce color picture tubes. The tubes thus produced are then tested. Then the process as above described is repeated in accordance with the method of trial and error until correction lenses for each color are produced for mass production. This measure, however, consumes a great deal of time and much labor.

Once a particular correction lens has been produced for printing the phosphor mosaic for each of the primary colors on the face plate of shadow mask color picture tubes, it is desirable to provide a simple means for slightly and at least locally varying a pattern in which phosphor dots for each of the primary colors are disposed on the face plate from that provided by that correction lens without modifying the latter.

To this end, the invention includes winding means phosphor screen, and means for supplying a high frequency current of a suitable waveform to the winding means to heat a shadow mask disposed inside of the face plate through electromagnetic induction to thereby temporarily slightly deform the shadow mask into a desired shape while a forming beam of radiation irradiates the face plate through the holes on the slightly deformed shadow mask.

Referring now to FIG. 3 wherein like reference numerals designate the components identical to those shown in FIG. 1, it is seen that an arrangement disclosed herein comprises, in addition to the apparatus as shown in FIG. 1, a flat winding 40 disposed adjacent to and externally of the face plate 18 and substantially perpendicularly to the longitudinal axis of the apparatus, and a high frequency oscillator 42 for supplying a high frequency current of suitable waveform to the winding 40 through a pair of flexible leads 44. The flat winding 40 is attached to a holding plate 46 connected to an upright arm 48 which is, in turn, fixed to the framework 10 whereby the winding 40 'is maintained a predetermined distance from the face plate 18 and therefore from the shadow mask 22.

The holding plate 46 with the flat winding 40 may have preferably an operating position where the winding 40 directly opposes the face plate 18 and an inoperative position turned through an angle of about 90 degrees from the operative position as shown at dotted lines 46a and 40a in FIG. 3. This measure facilitates the movement of the winding-plate assembly 40 46 from one to the other of its positions.

The flat winding 40 may be preferably in the form of a single flat coil centered relative to the face plate 18 with all sides thereof substantially parallel to the adjacent edges of the face plate as shown in FIG. 4a. Alternatively it may be in the form of two serially connected coils disposed substantially in parallel to each other and to the adjacent edges of the face plate 18 and equidistant from the vertical axis of the latter as shown in FIG. 4b.

It has been found that, with satisfactory results, the high frequency oscillator 42 produces a current at a frequency ranging from several to tens of kilohertz and has an output voltage and an output impedance, includ- 1 shown in FIG. 3.

FIG. 5 shows by way of example a shadow mask deformed by heating it by the arrangement of FIG. 3 having suitably adjusted parameters. Before the shadow mask is heated with a high frequency current from the oscillator 42, the same has a cross sectionalprofile as shown at dotted line 22 including holes represented by the reference numeral 50. A beam portion of ultraviolet radiation 52 from a point source such as the source 14 shown in FIG. 3 or 1, passes for example, through the hole 50 on the shadow mask 22 until it impinges upon the layer of phosphor slurry 20 at the associated point 54 on the face plate 18.

On the other hand, when the shadow mask is being heated with a high frequency current from the oscillator 42, it has a cross sectional profile as shown at solid line 22a and therefore the holes thereon are displaced. For example, the hole 50 is displaced to its position 50a as shown in FIG. 5. As a result, another beam portion of ultraviolet radiation 52a slightly different in direction from the beam portion 52 is permitted to pass through the displaced hole 50a to impinge upon the layer at a position 54a also displaced from the initial position 54. Thus a latent image for phosphor dots is formed at the position 54a on the slurry layer 20.

Therefore it will be appreciated that the invention provides a means to displace positions where corresponding phosphor dots are to be printed on the face plate, for example from the point 54 to the point 54a.

Windings such as shown in FIGS. 4a and 4b were used to heat shadow masks in the manner as above described in conjunction with FIGS. 3 and 5,'thereby to print a phosphor mosaic on the associated face plates of color picture tubes. Also phosphor mosaics were printed on similar face plates without heating the associated shadow masks. By comparing the resulting phosphor mosaics with each other, it has been seen that with the shadow mask heated, the phosphor dots printed on the face plates are displaced substantially toward the center of the face plate as shown at the arrows in FIGS. 6a and 612. FIG. 6a shows the directions in which the phosphor dots are displaced on the face plate 18 for the winding such as shown in FIG. 4a and dotted line designates the profile of the winding. FIG. 6b is a view similar to FIG. 6a but depicts the arrangement of FIG. 4b. It has been found that the region over which the printed phosphor dots are displaced has a profile as approximately determined by both the profile of the winding involved and the distance between the winding and face plate and that the magnitudes of displacement of the phosphor dots printed within the region as above described are determined by a distribution of convolutions of the winding, the magnitude and a waveform of the high frequency current supplied to the winding, etc. This means that any phosphor dot printed on the face plate may be displaced toward the center of the face plate by any desired magnitude substantially in every region of the face plate.

In addition, if the arrangement of FIG. 3 includes the point source l4 disposed at any position different from its position as illustrated in FIG. 3 then the phosphor dots can be printed on the face plate at positions displaced outwardly or inwardly relative to the center of the face plate by any desired magnitude in almost every area of the face plate with respect to their positions where the dots would be printed on the plate without the shadow mask heated in accordance with the present invention. Those directions in which the phosphor dots are displaced outwardly or inwardly from the center of the face plate may be called hereinafter the radial directions." In this connection it is noted that almost all the benefits of a modified correction lens are necessarily accomplished resulting from the fact that those positions where the associated phosphor dots are to be printed on the face plate are varied in the radial directions as above specified. It is also noted that such a correction lens is naturally effective only for radially displacing those positions where phosphor dot are printed on the face plate. On the other hand, it may be required to displace the printing positions for phosphor dots in the circumferential direction of the face plate or direction perpendicular to the radial directions thereof. In the latter case, the correction lens is not so effective and therefore separate means should be utilized.

The invention has several advantages. For example, the invention is substantially identical in effectiveness to a change in design of a correction lens invoved and yet provides a means to immediately effect the determination of the configuration of the heatingwinding and the control of a current supply to the winding while shadow mask color-picture tubes are being manufactured for testing. This eliminates the cost and delay previously experienced for the correction lens to be changed in design. Further the invention makes it possible to effect any complicated correction for positions of phosphor dots on the face plate through the use of a correction lens simple in structure. Correction lenses have generally complicated surfaces such as nonspheric or asymmetric surfaces are expensive and also take a long time to manufacture. However, it is possible to substitute rotation-symmetric non-spherical surfaces or even spherical surfaces for such complicated surfaces and to effect the required residual correction in accordance with the method of the invention. Moreover, the invention provides a means to correct the positions for phosphor dots printed on the face plate even without the necessity of using any correction lens.

Also, in order to improve the contrast of pictures developed on the phosphor screen of shadow mask color picture tubes, it has been already proposed to produce phosphor screens of the type including color phosphor dots located in a predetermined pattern thereon and a layer of non-luminescent black material such as graphite filling spaces between the color phosphor dots. FIGS. 7a and 7b show one portion of such a phosphor screen in plan and in cross section respectively. As shown, a layer of graphite as the non-luminescent black material fills spaces between color phosphor dots 72 to form a three-color phosphor screen on an internal surface of a face plate 18.

Phosphor screens such as shown in FIGS. 7a and 711 have been generally formed in accordance with the following steps: First, a face plate such as previously described in conjunction with FIGS. 1 through 3 is coated with any suitable photosensitive material called a photoresist to form a photoresist layer on the internal surface thereof. FIG. 8a illustrates the resulting structure including the photoresist layer 60 disposed on the glass face plate 18. r

A second step is to expose the photoresist layer 60 on the face plate l8 to a beam of ultraviolet radiation through the associated shadow mask three times; one for each of three primary colors or red, green, and blue through the utilization of the apparatus as shown in FIG. I. The beam portions of ultraviolet radiation passed through the holes on the shadow mask fall upon the associated elementary areas of the photoresist layer to form a latent image for each of the red, green and blue phosphors.

The succeeding or third step is to wash the face plate separated from the shadow mask with water to remove the unexposed portion of the photoresist layer leaving photoresist dots 62 in a predetermined pattern on the internal surface thereof as shown in FIG. 8b.

In a fourth step, an aqueous suspension of nonluminescent black material, in this case, graphite in the form of finely divided particles is sprayed upon the internal surface of the face plate 18 with the photoresist dots 62 to form a graphite layer to completely cover the dots. The resulting structure is shown in FIG. 8c wherein the face plate 18 is illustrated as having the graphite layer 70 disposed on the internal surface thereof with the photoresist dots 62 fully embedded in the layer 70.

The succeeding, fifth step is to partly remove the graphite layer 70 from the face plate 18 to expose those portions of the internal face surface on which the photoresist dots 62 are disposed. To this end, water containing hydrogen peroxide is first sprayed noon the graphite layer 70 to penetrate through the latter to thereby decompose the photoresist dots. Therefore the adhesion between the glass forming the face plate and those portions of the graphite layer underlaid by the decomposed dots decreases. Then the face plate is washed with water to remove the graphite portions decreased in adhesion to the glass or underlaid by the photoresist dots, from the face plate. As shown in FIG. 8d, the resulting structure includes the graphite layer 70 and elementary blank areas 71 disposed on the internal surface of the face plate 18 in the same pattern as the photoresist dots.

The face plate thus prepared is processed in the manner as previously described in conjunction with FIG. 1 to print the desired phosphor dots 72 at the blank areas 71 resulting in the arrangement as shown in FIG. 7.

By comparing a shadow mask color picture tube including the phosphor screen as described in conjunction with FIG. 8, with those not including such a phoswith satisfactory results. More specifically, the second phor screen, it has been found that the two types of tubes are not materially different in operation from each other. This means that, for shadow mask color picture tubes including the non-luminescent black material filling the spaces between color phosphor dots, the positions of blank areas 71 or the positions of photoresist dots 62 to be disposed on the internal surface of the face plate are significant for the operation of the tube as are the positions of color phosphor dots.

Thus the invention is equally applicable to the second step as above described in conjunction with FIG. 8,

step can effectively proceed by using the apparatus as shown in FIG. 3. Thereafter color phosphor dots are printed at the blank areas of the layer of nonluminescent material inthe manner as previously described in conjunction with FIG. 3.

What we claim is:

1. In a process of forming a mosaic phosphor screen i on the face plates of shadow mask color picture tubes, including the steps of applying a phosphor coating to one side of a face plate, positioning a shadow mask over the phosphor coating on said face plate, selecthe step of positioning a correction lens between the,

point source and the shadow mask for adjusting the path travelled by the beam of radiation.

3. The improvement of claim 1 comprising the further steps of first forming a layer'of non-luminescent black material on the internal surface of the face plate, said layer having blank spots therein; and then printing color phosphor dots on the blank area of the layer of non-luminescent black material. 

1. IN A PROCESS OF FORMING A MOSAIC PHOSPHOR SCREEN ON THE FACE PLATES OF SHADOW MASK COLOR PICTURE TUBES, INCLUDING THE STEPS OF APPLYING A PHOSPHOR COATING TO ONE SIDE OF A FACE PLATE, POSITIONING A SHADOW MASK OVER THE PHOSPHOR COATING ON SAID FACE PLATEN, SELECTIVELY EXPOSING THE COATING TO A BEAM OF ULTRAVIOLET RADIATION EMITTED FROM A POINT SOURCE THROUGH HOLES IN THE SHADOW MASK, AND PROCESSING THE EXPOSED COATING TO FORM A MOSAIC OF PHOSPHOR DOTS IN A PREDETERMINED PATTERN ON THE INTERNAL SURFACE OF THE FACE PLATE, THE IMPROVEMENT WHICH COMPRISES: HEATING THE SHADOW MASK TO CAUSE A PREDETERMINED DEFORMATION THEREOF; AND SIMULTANEOUSLY IRRADIATING THE LAYER OF PHOSPHOR MATERIAL THROUGH THE HOLES IN THE THUS DEFORMED SHADOW MASK.
 2. The improvement of claim 1 further comprising the step of positioning a correction lens between the point source and the shadow mask for adjusting the path travelled by the beam of radiation.
 3. The improvement of claim 1 comprising the further steps of first formiNg a layer of non-luminescent black material on the internal surface of the face plate, said layer having blank spots therein; and then printing color phosphor dots on the blank area of the layer of non-luminescent black material. 